where I ended up looking up old census records for Ann Arbor when talking about the birth of college football, and I'd love to see what State or Main or Packard, M campus generally or downtown generally looked like when the population was 20,000.

The Bentley rocks for things like this. Have you checked out their image bank? It's open to the public. Just search for "Ann Arbor Main Street" or whatever and all kinds of interesting pictures come up.

I was an undergrad engineering student then, so I walked by the building a lot of times going to class in East and West Engineering and the chemistry building. IIRC, it was around 1980 or 1981 when it caught fire.

It was a strange building within the diag. White rather than brick, and small and more house-like than the surrounding buildings. I thought it always looked out of place.